Light emitting device

ABSTRACT

A light-emitting device is disclosed with improved luminance even with increased arrangement density of a reflector regardless of a light-emitting region. The disclosed device includes a reflector between an electrode for extracting light from a layer including a luminescent material, which serves as a light-emitting region of a light-emitting element, and an exterior space (air). In addition, a light-extraction efficiency can be improved by setting an angle made by a surface of the reflector, which faces the light-emitting element, and a side surface of the reflector (hereinafter, referred to as a slope angle of the reflector) in a predetermined range as for a shape of the reflector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improving a luminance of alight-emitting device that has a light-emitting element.

2. Description of the Related Art

A light-emitting element that is thin in thickness, light in weight, hasa high speed response, and uses a low DC driving voltage has beenexpected to be applied to a next-generation flat panel display. Inparticular, a light-emitting device that has light-emitting elementsarranged in a matrix shape is considered to be superior in having a wideview angle and a high level of visibility, as compared to a conventionalliquid crystal display device.

A light-emitting element is said to have an emission mechanism whereinan electron and a hole respectively injected from a pair of electrodesare recombined in the luminescence center of a layer includingluminescent material to form an excited molecule when a voltage isapplied to the layer including the luminescent material between the pairof electrodes. Energy is released to emit light when the excitedmolecule moves back toward the ground state. Both a singlet excitedstate and a triplet excited state are known, and luminescence is said tobe possible through either of them.

When light-emitting elements are arranged in a matrix, the drivingmethod can be passive matrix driving (a simple matrix type) or activematrix driving (an active matrix type). When the pixel density is high,an active matrix type in which a switch is provided for each pixel (oreach dot) is considered to be advantageous since low-voltage driving ispossible.

One problem in such a light-emitting device is that light can beextracted insufficiently from the light-emitting element. One mayprovide a reflector for improving a light-extraction efficiency. It isreported, for example, that a wiring of a TFT is used as alight-reflector. For example, refer to Patent Document 1. It is alsoreported that a metal film is formed into a portion of a substrate inadvance. For example, refer to Patent Documents 1 and 2.

(Patent Document 1)

Japanese published unexamined application No. 2002-229482

(Patent Document 2)

Japanese published unexamined application No. 2002-352950

However, in the foregoing cases, a structure that has the reflectorarranged in a position overlapped with a light-emitting region of alight-emitting layer is used when extracting light from the side wherethe reflector is arranged. Therefore, when an arrangement density of thereflector is made higher, the luminance is not improved since thelight-emitting region is narrowed, while the light-extraction efficiency(light intensity extracted outside/light intensity emitted from thelight-emitting region) is improved. Alternatively, when the arrangementdensity of the reflector is made lower to expand the light-emittingregion, the light-extraction efficiency is decreased since light emittedfrom the light-emitting region cannot be reflected by the reflector somuch, with the result that luminance is not improved. The arrangementdensity of the reflector is a ratio of an area of the reflector providedin a position overlapped with a light-emitting surface of alight-emitting layer to an area of the light-emitting region of thelight-emitting layer. This ratio may be considered as that of an area ofthe reflector provided in a position overlapped with a light-emittingsurface of a light-emitting layer to an area of the light-emittingregion of the light-emitting layer in a pixel.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light-emittingdevice that is capable of improving luminance despite increasing anarrangement density of a reflector independently of a light-emittingregion.

According to one aspect of the present invention, it is one of featuresto provide a reflector between an electrode for extracting light from alayer including a luminescent material, which serves as a light-emittingregion of a light-emitting element, and an exterior space (air).According to another aspect of the present invention, thelight-extraction efficiency can be improved by controlling an angle madeby a surface of the reflector, which faces the light-emitting element,and a side surface of the reflector (hereinafter, referred to as a slopeangle of the reflector) to be in a predetermined range. In the case offorming the reflector in a portion of an insulating film, the reflectorand the insulating film share a common surface. Further, alight-extraction efficiency can be improved by setting the arrangementdensity thereof in a preferred range.

In addition, also by setting a shape parameter of the reflector such asa height of the reflector or a width of the reflector, or an arrangementparameter of the reflector such as an arrangement distance of thereflector or a distance between the reflector and a reflective electrodein a desired range, the light-extraction efficiency can be improved. Onereflector may be formed continuously all over the pixel portion. Also,each pixel may have a reflector therein. Further, a plurality ofreflectors may be formed in each pixel.

In other words, the present invention provides a light-emitting devicethat has a light-emitting element over a substrate, wherein thelight-emitting element includes a first electrode, a layer including aluminescent material, and a second electrode. The first electrode istransparent, a reflector is provided between the substrate and the firstelectrode, and the reflector is provided in a position overlapping (atleast partially) the first electrode.

In addition, in the light-emitting device, in the case where thereflector is formed in a portion of an insulating film formed over thesubstrate, and the reflector and the insulating film share a commonsurface, when the layer including the luminescent material has arefractive index n₁ and the insulating film has a refractive index n₂,the reflector has a slope angle φ:

when n₁≧n₂,φ=45+(½)sin⁻¹(1/n ₂)±10(°); and

when n₁<n₂,φ=90−(½){sin⁻¹(n ₁ /n ₂)−sin⁻¹(1/n ₂)}±10(°) (n₁ and n₂=1 to 3)

Further, the layer including the luminescent material has a refractiveindex n₁, the reflector has a reflectance r₁, and the second electrodehas a reflectance r₂, the reflector has an arrangement density x:x<cos{sin⁻¹(1/n ₁)}/[1−r ₁ r ₂[1−cos{sin⁻¹(1/n ₁)}]](n₁=1 to 3 and 0.5<r₁, r₂<1.0).

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams illustrating an arrangement and a structureof a reflector according to certain aspects of the present invention;

FIGS. 2A and 2B are diagrams showing a result of a simulation of areflector;

FIGS. 3A and 3B are diagrams showing a result of a simulation of areflector;

FIGS. 4A and 4B are diagrams showing a result of a simulation of areflector;

FIGS. 5A and 5B are diagrams illustrating shapes of a reflector;

FIG. 6 is a diagram showing results of a simulation with a reflector anda simulation without a reflector;

FIGS. 7A and 7B are diagrams illustrating an active matrixlight-emitting device;

FIGS. 8A and 8B are diagrams illustrating a light-emitting device; and

FIGS. 9A to 9G are diagrams illustrating electronic devices.

DETAILED DESCRIPTION OF THE INVENTION

(Embodiment Mode)

Aspects of the present invention are described with reference to FIG.1A. This shows a structure that has a reflector 102 in a portion of afirst insulating film 101 formed over a substrate 100, where thesubstrate 100 can transmit light, and the reflector 102 is providedbetween an electrode (a transparent electrode 105) for extracting lightfrom a light-emitting element 108 formed over a second insulating film104 and an exterior space (air). The light-emitting element 108 includesthe transparent electrode 105, a layer 106 including a luminescentmaterial, and a reflective electrode 107.

FIG. 1B shows a structure of the reflector 102 shown in FIG. 1A, whichis viewed from the light-emitting element 108 side. Here, an example ofthe reflector 102 having a hexagonal opening 110 is shown. However, anyshape, such as a quadrangle shape or a triangular shape, can be appliedas long as the reflector of the same shape 102 can be formed repeatedly.It will be understood that the reflector 102 shares a common surfacewith the upper surface of insulating film 101 in FIG. 1A.

Next, a preferable shape of a reflector for improving an extractionefficiency of light obtained from a light-emitting element will beconsidered.

First, a preferable slope angle of a reflector will be considered. Whenlight is emitted from a layer including a luminescent material(refractive index: n₁) at an angle (angle of emergence: θ₁), the lightis made to enter an insulating film (refractive index: n₂) at an angle(angle of incidence: θ_(i)).

In this case,n₁ sin θ₁=n₂ sin θ_(i)is effected in accordance with Snell's law.

Since light is emitted in all directions from the layer including theluminescent material,−90°≦θ₁≦90°.

Therefore, when n₁≧n₂,−90°≦θ_(i)≦90°, and

when n₁<n₂, $\begin{matrix}{{- {\sin^{- 1}( \frac{n_{1}}{n_{2}} )}} \leq \theta_{i} \leq {\sin^{- 1}( \frac{n_{1}}{n_{2}} )}} & (1)\end{matrix}$

On the other hand, when the light that has entered the insulating film(refractive index: n₂) is reflected by the reflector and emitted at anangle (angle of emergence: θ_(r)), the light enters the air (refractiveindex: 1) at an angle (angle of incidence: θ_(a)).

In this case also,n₂ sin θ_(r)=sin θ_(a)is effected in accordance with Snell's law.

When the light is emitted into the air, θ_(r) has a range of$\begin{matrix}{{- {\sin^{- 1}( \frac{1}{n_{2}} )}} \leq \theta_{r} \leq {\sin^{- 1}( \frac{1}{n_{2}} )}} & (2)\end{matrix}$

Further, from the relationship between a slope angle (φ) of thereflector and the angle (θ_(r)) of the light reflected by the reflector(φ′=90°−φ),θ_(i)−φ′=φ′−θ_(r)Accordingly,θ_(r)=2φ′−θ_(i)  (3)is effected.

So that the light that has entered the insulating film should bereflected by the reflector and extracted into air, it is necessary tosatisfy−sin⁻¹(1/n₂)≦θ_(r)≦sin⁻¹(1/n₂)Accordingly,−sin⁻¹(1/n ₂)≦2φ′−θ_(i)≦sin⁻¹(1/n ₂)Consequently, $\begin{matrix}{{{2\phi^{\prime}} - {\sin^{- 1}( \frac{1}{n_{2}} )}} \leq \theta_{i} \leq {{2\phi^{\prime}} + {\sin^{- 1}( \frac{1}{n_{2}} )}}} & (4)\end{matrix}$from Formula 2 and Formula 3.

In addition, the condition for the light with θ_(i) on a reflectivesurface of the reflector is expressed byφ′<θ_(i)≦θ_(i max)  (5)

In Formula 5,

-   -   when n₁≧n₂,        θ_(i max)=90°, and    -   when n₁<n₂,        θ_(i max)=sin⁻¹(n ₁ /n ₂)

Here, since θ_(i) that satisfies Formula 5 also satisfies Formula 4,$\begin{matrix}{{{2\phi^{\prime}} - {\sin^{- 1}( \frac{1}{n_{2}} )}} \leq \phi^{\prime}} & (6) \\{\theta_{i\quad\max} \leq {{2\phi^{\prime}} + {\sin^{- 1}( \frac{1}{n_{2}} )}}} & (7)\end{matrix}$

From Formula 6 and Formula 7, $\begin{matrix}{{\frac{1}{2}\lbrack {\theta_{i\quad\max} - {\sin^{- 1}( \frac{1}{n_{2}} )}} \rbrack} \leq \phi^{\prime} \leq {\sin^{- 1}( \frac{1}{n_{2}} )}} & (8)\end{matrix}$is effected, and from φ′=90°−φ, $\begin{matrix}{{90 - {\sin^{- 1}( \frac{1}{n_{2}} )}} \leq \phi \leq {90 - {\frac{1}{2}\lbrack {\theta_{i\quad\max} - {\sin^{- 1}( \frac{1}{n_{2}} )}} \rbrack}}} & (9)\end{matrix}$can be obtained.

As the slope angle φ is larger, an arrangement density of the reflectorcan be lowered, and a light-extraction efficiency can be increased.Therefore, the slope angle φ of the reflector in the present inventionis expressed by $\begin{matrix}{\phi = {90 - {\frac{1}{2}\lbrack {\theta_{i\quad\max} - {\sin^{- 1}( \frac{1}{n_{2}} )}} \rbrack}}} & (10)\end{matrix}$

In Formula 10,

-   -   when n₁≧n₂,        φ=45+(½)sin⁻¹(1/n ₂)(°), and    -   when n₁<n₂,        φ=90−(½){sin⁻¹(n ₁ /n ₂)−sin⁻¹(1/n ₂)}(°)        In addition, in Formula 10, it is preferable that n₁ and n₂=1 to        3.

In other words, a preferable slope angle (φ) of a reflector in thepresent invention is expressed by Formula 10.

Hence, according to one aspect of the present invention, alight-emitting device that is capable of improving an extractionefficiency of light from a light-emitting element can be formed byproviding a reflector between the light-emitting element and an exteriorspace, and further setting a slope angle of the reflector in the rangeshown by Formula 10.

Further, in accordance with the present invention, an arrangementdensity of the reflector will be considered. When the arrangementdensity is set at x (0<x<1), a portion (1−x) of light having entered asurface in which the reflector is formed is transmitted through a regionin which no reflector is arranged to enter an interface between asubstrate and the air. On the other hand, the other portion x of thelight is reflected repeatedly between a flat surface of the reflectorand a reflective electrode and then is transmitted through the region inwhich no reflector is located to enter the interface 111 between thesubstrate and the air.

By being reflected by the reflector and the reflective electrode, thelight has an intensity attenuated r₁ times (where r₁ is a reflectance ofthe reflector, and where 0<r₁≦1) and r₂ times (r₂ is a reflectance ofthe reflective electrode, 0<r₂≦1), respectively. In addition, sincelight is emitted from a light-emitting layer isotropically in alldirections, one half of the light is emitted toward the reflector andthe other half is emitted toward the reflective electrode.

Consequently, a proportion T of light emitted from a light-emittinglayer, which is transmitted through the region in which no reflector isarranged to enter the interface between the substrate and the air, isexpressed by: $\begin{matrix}{T = {{\frac{1}{2}{\sum\limits_{i = 0}^{\infty}{( {1 - x} )( {{xr}_{1}r_{2}} )^{i}}}} + {\frac{1}{2}r_{2}{\sum\limits_{i = 0}^{\infty}{( {1 - x} )( {{xr}_{1}r_{2}} )^{i}}}}}} & (11) \\{T = \frac{( {1 + r_{2}} )( {1 - x} )}{2 \cdot ( {1 - {r_{1}r_{2}x}} )}} & (12)\end{matrix}$

Even when the light transmitted through the region in which no reflectoris arranged is all extracted into air, the extraction efficiency cantake only a value given by Formula 12 at a maximum.

On the other hand, an extraction efficiency T₀ in the case of arrangingno reflector is expressed by: $\begin{matrix}{T_{0} = {\frac{1}{2}{( {1 + r_{2}} )\lbrack {1 - {\cos( {\sin^{- 1}( \frac{1}{n_{1}} )} )}} \rbrack}}} & (13)\end{matrix}$

In order to improve an extraction efficiency by using a reflector, fromFormula 12 and Formula 13,(1+r ₂)(1−x)/{2(1−r ₁ r ₂ x)}>(1+r ₂)[1−cos{sin⁻¹(1/n ₁)}]/2

Consequently, $\begin{matrix}{x < \frac{\cos( {\sin^{- 1}( \frac{1}{n_{1}} )} )}{1 - {r_{1}{r_{2}\lbrack {1 - {\cos( {\sin^{- 1}( \frac{1}{n_{1}} )} )}} \rbrack}}}} & (14)\end{matrix}$

In addition, it is preferable that n₁=1 to 3, and 0.5<r₁, r₂<1.0 in theaforementioned Formula 13.

That is, a preferable arrangement density (x) of a reflector accordingto this aspect of the present invention is expressed by Formula 14.

In other words, it is preferable to provide a reflector between alight-emitting element and an exterior space, and further set anarrangement density of the a reflector in the range shown by Formula 14in order to improve an extraction efficiency of light from thelight-emitting element.

For example, when n₁=1.5 and r₁=r₂=0.92, it is preferable to set anarrangement density x<0.95.

Hereinafter, embodiments of the present invention will be described.

Embodiment 1

In the present embodiment, a simulation of preferable shape andarrangement of a reflector for improving an extraction efficiency oflight obtained from a light-emitting element will be described.

As a model structure of a light-emitting device to be used for thesimulation. FIG. 2A shows or represents a first insulating film 202,having a refractive index of 1.5, a reflector 203 having a reflectanceof 92%, a second insulating film 204 having a refractive index of 1.5,and a light-emitting element 205 laminated over a glass substrate 201having a refractive index of 1.5. The light-emitting element 205includes a first electrode 206, a light-emitting layer 207 having arefractive index of 1.5, and a second electrode 208. When the secondelectrode 208 serves as a reflective electrode, its reflectance ispreferably arranged to be 92%.

For the simulation, a ray tracing simulator such as Light-Tools fromOptical Research Associate is used to trace light (illustratively, 5000rays) emitted from random positions in the light-emitting layer of thelight-emitting element isotropically in all directions by means of adetector disposed outside the glass substrate. In this case, only atotal reflection is considered while a reflection at an interfacebetween layers that have different refractive indexes from each other(the glass substrate/air) is ignored.

First, a simulation of a slope angle of the reflector was conducted.Here, a height (h) of the reflector, an arrangement interval (I) of thereflector, and a distance (d) between the reflector and the reflectiveelectrode are set 1 μm, 3 μm, and 2 μm, respectively, and changes inextraction efficiency are measured for various slope angles of thereflector. FIG. 2B shows the results in one case where the firstinsulating film has a refractive index of 1.5 and in a second case wherethe first insulating film has a refractive index of 2.0.

According to the results of FIG. 2B, in the case of the refractive indexof 1.5, the maximum extraction efficiency (52%) is obtained when theslope angle of the reflector is set at 60°. On the other hand, in thecase of the refractive index of 2.0, the maximum extraction efficiency(36%) is obtained when the slope angle of the reflector is set at 80°.The extraction efficiency in the case where there is no reflector is25%. Therefore, when the extraction efficiency is 25% or more in thepresent invention, this improvement can be attributed to the reflector.In other words, it is preferable that the slope angle of the reflectorbe set from 40° to 80° when the first insulating film 202 has arefractive index of 1.5 and the slope angle be set from 60° to 85° whenthe first insulating film 202 has a refractive index of 2.0.

Accordingly, it is preferable that a reflector in the present inventionhas a slope angle (φ) in the following range, that is, (the range shownby Formula 10 in Embodiment Mode) ±10°.

In other words, when a layer including a luminescent material has arefractive index n₁ and an insulating film has a refractive index n₂, itis preferable that:

-   -   when n₁≧n₂,        φ=45+(½)sin⁻¹(1/n ₂)±10(°); and    -   when n₁<n₂,        φ=90−(½){sin⁻¹(n ₁ /n ₂)−sin⁻¹(1/n ₂)}±10(°)        (n₁ and n₂=1 to 3).

Embodiment 2

Next, a simulation of a relationship between a width (w) of a reflectorand a distance (d) between the reflector and a reflective electrode wasconducted in order to obtain a preferable range for improving theextraction efficiency. The measurement was conducted in the same way asEmbodiment 1.

Here, a height (h) of the reflector, an arrangement interval (I) of thereflector, and a width (w) of the reflector are set 1 μm, 3 μm, and 1.15μm, respectively, as shown in FIG. 3A, and changes in extractionefficiency are measured for various ratios (Y) of the distance betweenthe reflector and the reflective electrode to the width of the reflector(=the distance between the reflector and the reflective electrode(d)/the width of the reflector (w)). In FIG. 3A, reference numerals 301,302, and 307 denote a first insulating film, the reflector, and thereflective electrode, respectively. FIG. 3B shows the results where thefirst insulating film has a refractive index of 1.5.

According to FIG. 3B, the extraction efficiency is always 25% or more,indicating that an effect due to providing the reflector has beenobtained. In the present embodiment, the extraction efficiency is 40% ormore is regarded as more preferable. In other words, it is preferablethat the ratio (Y) of the distance between the reflector and thereflective electrode to the width of the reflector be controlled to be0.1 or more. The reason for this is that with the aforementionedconditions (the height (h) of the reflector is 1 μm, the arrangementinterval (I) of the reflector is 3 μm, and the width (w) of thereflector is 1.15 μm), the extraction efficiency is 40% or more when theratio (Y) of the distance between the reflector and the reflectiveelectrode to the width of the reflector is controlled to be 0.1.

Embodiment 3

Next, a simulation of an arrangement density (x) of a reflector isconducted in order to obtain a preferable range for improving extractionefficiency. Here, the height (h) of the reflector, and the distance (d)between the reflector and a reflective electrode are controlled to be 1μm and 2 μm, respectively, as shown in FIG. 4A, and changes inextraction efficiency are measured for various arrangement densities (x)of the reflector. The arrangement density (x) of the reflector means aratio of an area of the reflector provided in a position overlapping alight-emitting surface of a light-emitting layer to an area of thelight-emitting surface of the light-emitting layer. In FIG. 4A,reference numerals 401, 402, and 407 denote a first insulating film, thereflector, and the reflective electrode.

According to the result of FIG. 4B, the extraction efficiency is 25% ormore when the arrangement density (x) of the reflector is set at 0.95 orless (95% or less in FIG. 4B shown in percentage). In the presentinvention, the effect of providing this is beneficial when theextraction efficiency is 25% or more. Therefore, the arrangement densityof the reflector should be controlled to be 0.95 or less, morepreferably, from 20 to 80%, in the aforementioned condition (the height(h) of the reflector is 1 μm and the distance (d) between the reflectorand a reflective electrode is 2 μm).

Embodiment 4

The present invention does not require the opening of the reflector tobe hexagonal. FIGS. 5A and 5B show some cases where the opening hasdifferent shapes from the hexagonal shape shown in FIG. 1B.

FIG. 5A shows a reflector 501 that has openings 502 in the shape of aquadrangle. This shape makes it possible to form the reflector in adesired position without any gap, and therefore can be used for areflector according to the present invention.

In addition, FIG. 5B shows a reflector 503 that has openings 504 in atriangular shape. Since the reflector can be formed in a desiredposition without any gap also in the case of this shape, this shape canbe used for a reflector according to the present invention.

The reflector in the shape shown in the present embodiment can bearranged over an insulating film (the first insulating film 101 in FIG.1A) formed over a substrate in the same way as the reflector shown inthe first-described “Embodiment Mode”.

Embodiment 5

The influence on extraction efficiency of light from a light-emittingelement due to the presence or absence of an arrangement of a reflectorwill be described.

In the present embodiment, the same structure shown in FIG. 1A is used.The first insulating film 101 and the second insulating film each have arefractive index of 1.5. The reflective electrode 107 and the reflector102 each have a reflectance of 92% and an absorbance of 8%. Thearrangement of the reflector is as shown in FIG. 1B.

FIG. 6 shows the distributions of light emission for the arrangementboth with and without a reflector. This figure shows clearly that thereis a difference in the distribution of light emission depending on apresence or absence of the reflector. Specifically, by providing thereflector, the light intensity in the direction of the front side isincreased approximately threefold as compared to the case without thereflector provided.

In addition, the light-extraction efficiency is 25% without thereflector provided. However, by providing the reflector, thelight-extraction efficiency becomes 51%, which is approximately double.

Hence, the light-extraction efficiency is spectacularly improved byproviding the reflector.

Embodiment 6

In the present embodiment an active matrix light-emitting device will bedescribed.

With reference to FIG. 7A, a case of forming a reflector according tothe present invention before forming a TFT (thin film transistor)electrically connected to a light-emitting element will be described.

First, a first insulating film 701 is formed on a substrate 700. As amaterial for forming the first insulating film 701, an insulating filmincluding silicon such as silicon oxide, silicon nitride, or siliconoxynitride can be used.

Next, photolithography is used to form a groove 713, thereby forming aportion surrounded by the groove in a portion of the first insulatingfilm 701 in order to form a reflector. Then, a film containing areflective material is formed over the first insulating film 701including the opening. It is preferable that the reflective materialthat is used here has a reflectance of 50% or more in a visible lightrange, and more preferably, a material that has a reflectance of 80% ormore is used. Specifically, a material such as silver (Ag), aluminum(Al), tantalum (Ta), niobium (Nb), molybdenum (Mo), copper (Cu),magnesium (Mg), nickel (Ni), or lead (Pb) is used.

After forming the reflective film, CMP (Chemical Mechanical Polishing)is used to polish the film comprising the reflective material untilexposing a surface of the first insulating film 701, and thereby, areflector 702 is formed.

Next, a TFT 703 is formed. The TFT has at least an impurity region (asource region or a drain region) 704, a channel-forming region 705, agate insulating film 706, and a gate electrode 707.

Although a plurality of TFTs are formed in the same layer, the TFT 703shown in FIG. 7A indicates a TFT electrically connected to a firstelectrode of a light-emitting element to be formed later (also referredto as a current controlling TFT). Then, an interlayer insulating film708 is formed to cover the TFT 703. Such film 708 can be formed (here)of a single layer using an insulating material, or alternatively, alaminated structure using a plurality of insulating materials can beused. The insulating material may comprise a material such as aninorganic material (such as silicon oxide, silicon nitride, or siliconoxynitride) or a photosensitive or non-photosensitive organic material(such as polyimide, acrylic, polyamide, polyimideamide, resist,benzocyclobutene, or SOG). In the present embodiment, the interlayerinsulating film 708 is formed of a laminated structure of a first layerof a silicon nitride film formed to have a film thickness of 100 nm anda second layer of acrylic formed to have a film thickness of 1.00 μm.

Next, after forming an opening in a portion of the interlayer insulatingfilm 708 and the gate insulating film 706 to reach the impurity region704 of the TFT 703, a wiring 709 is formed by depositing and patterninga conductive film. The wiring material may comprise an element selectedfrom Ta, W, Ti, Mo, Al, and Cu, or one of an alloy material and acompound material including the element as its main component. In thepresent embodiment, a film of formed by sequentially laminating atantalum nitride film with the film thickness of 30 nm and a tungstenfilm with the film thickness of 370 nm is used.

Next, a first electrode 710 electrically connected to the wiring 709 isformed. In the present embodiment, a transparent conductive film is usedto form the first electrode 710. Since the first electrode 710 is anelectrode that functions as an anode, ITO (indium tin oxide) is used toform the first electrode 710 by sputtering to achieve a film thicknessof 110 nm.

Next, a layer 711 including a luminescent material is formed over thefirst electrode 710. Layer 711 may comprise a single-layer structure ofonly a light-emitting layer, or alternatively, may comprise a laminatedstructure using a plurality of materials. The layer 711 including theluminescent material in the present embodiment has a laminated structurecomprising a hole injection layer containing copper phthalocyanine(Cu-Pc), a hole transport layer containing4,4′-bis-[N-(naphtyl)-N-phenyl-amino]biphenyl (α-NPD), and alight-emitting layer containing tris-8-quinolinolato aluminum complex(Alq₃).

Next, a second electrode 712 is formed on the layer 711 including theluminescent material. It is preferable that the second electrode 712 hasa reflectance of 50% or more in a visible light range, and morepreferably, a reflective conductive film that has a reflectance of 80%or more is used to form the second electrode 712. Since, the secondelectrode 712 is an electrode that functions as a cathode, aluminum isused to form the second electrode 712 for a film thickness of 100 nm byevaporation using a metal mask. The material of the second electrode 712may comprise an alloy such as Mg:Ag, Mg:In, Al:Li, a compound such asCaF₂, or CaN, or a conductive film formed by co-evaporation of anelement belonging to Group 1 or 2 of the periodic table of the elementsand aluminum.

Further, in the case of a structure where light is transmitted alsothrough the second electrode 712, an aluminum film having a thicknessfrom 1 nm to 10 nm or an aluminum film including a slight amount of Lican be used. Before forming an aluminum film from 1 nm to 10 nm, alight-transmitting layer (a film thickness from 1 nm to 5 nm) containingCaF₂, MgF₂, or BaF₂ may be formed as a cathode buffer layer. In thiscase, a reflector according to the present invention can be providedalso over the second electrode 712.

In this way, an active matrix light-emitting device that has a reflectoraccording to the present invention is formed.

Further, it is also possible that an active matrix light-emitting devicein the present invention has a structure shown in FIG. 7B.

In other words, it is also possible to have a structure where a TFT 721is formed over a substrate 720, a reflector 724 and a wiring 726 areformed after forming a first interlayer insulating film 723 on a gateinsulating film 722, and a layer 729 including a luminescent materialand a second electrode 730 are laminated in sequence over a firstelectrode 728 electrically connected to the wiring 726 through a secondinterlayer insulating film 727 formed over the reflector 724 and thewiring 726.

No further descriptions are needed for the methods and materials formanufacturing the structure shown in FIG. 7B, descriptions are omittedsince the structure of FIG. 7B can be formed by using the same materialsin the same way as the structure of FIG. 7A.

Embodiment 7

In the present embodiment, a light-emitting device formed according tothe present invention, which has a light-emitting element in a pixelportion, will be described with reference to FIGS. 8A and 8B. FIG. 8A isa top view showing the light-emitting device and FIG. 8B is a sectionalview of FIG. 8A taken along the line A-A′ in FIG. 8A. Reference numeral801 indicated by a dotted line denotes a driver circuit portion (asource side driver circuit), 802 is a pixel portion, and 803 is a drivercircuit portion (a gate side driver circuit). In addition, referencenumerals 804 and 805 denote a sealing substrate and a sealing agent,respectively. The inside 807 (see FIG. 8B) surrounded by the sealingagent 805 is a space, and reference numerals 808 and 819 denote a leadwiring and a reflector, respectively.

The lead wiring 808 is provided for transmitting signals to be input tothe source side driver circuit 801 and the gate side driver circuit 803,and receives signals such as a video signal, a clock signal, a startsignal, and a reset signal, from FPC (Flexible Printed Circuit) 809 thatserves as an external input terminal. Though only the FPC is shown inthe figure here, a printed wiring board (PWB) may be attached to theFPC. The light-emitting device in the specification includes not only alight-emitting device body but also may have an FPC or a PWB attachedthereto.

Next, the sectional structure will be explained with reference to FIG.8B. The driver circuits and the pixel portion are formed over a devicesubstrate 810. Here, the source side driver circuit 801 as the drivercircuit portion and the pixel portion 802 are shown.

In the source side driver circuit 801, a CMOS circuit is formed of acombination of an n-channel TFT 823 and a p-channel TFT 824. The TFTsforming the driver circuit may be formed of a known CMOS circuit, PMOScircuit, or NMOS circuit. Although the present embodiment shows a driverintegrated type in which a driver circuit is formed over the substrate,which is not always necessary, the driver circuit can be formed outsidethe substrate.

The pixel portion 802 includes a plurality of pixels, each including aswitching TFT 811, a current controlling TFT 812, and a first electrode813 connected to the drain of the controlling TFT electrically. Inaddition, an insulator 814 is formed to cover an edge of the firstelectrode 813. Here, a positive photosensitive acrylic resin film isused to form the insulator 814.

On the first electrode 813, a layer 816 including a luminescent materialand a second electrode 817 are formed. Here, with the first electrode813 functioning as an anode, it is preferable that the material formingelectrode 813 should have a high work function. For example, theelectrode 813 may comprise single layers such as an ITO (indium tinoxide) film, an indium zinc oxide (IZO) film, a titanium nitride film, achromium film, a tungsten film, a Zn film, and a Pt film. It may alsocomprise structures such as a laminate of a titanium nitride film and afilm including aluminum as its main component and a three-layerstructure of a titanium nitride film, a film including aluminum as itsmain component, and a titanium nitride film. When a laminated structureis employed, the wiring has a low resistance, favorable ohmic contactcan be made, and it is possible to function as an anode. In the case ofthe present embodiment, ITO is used to form the first electrode 813.

The layer 816 including the luminescent material is formed byevaporation that uses an evaporation mask or by droplet dischargetypified by inkjet. The droplet discharge indicates a method ofdischarging a droplet including a predetermined composition from a poreto form a specific pattern. The layer 816 including the luminescentmaterial includes layers such as a light-emitting layer, a holeinjection layer, a hole transport layer, an electron injection layer,and an electron transport layer. In forming these layers, a lowmolecular weight material, a middle molecular weight material (includingan oligomer and a dendrimer) and a high molecular weight material can beused. In addition, it is often the case that an organic compound is usedfor a single layer or a laminate in the case of forming the layerincluding the luminescent material. However, the present inventionincludes a structure in which an inorganic compound is used for a partof a film containing an organic compound.

In addition, the second electrode (cathode) 817 formed on the layer 816including the luminescent material functions as a reflective electrode.The second electrode 817 may comprise aluminum (Al).

Further, the sealing substrate 804 and the substrate 810 are bonded withthe sealing agent 805 to obtain a structure where a light-emittingelement 818 is located in the space 807 surrounded by the substrate 810,the sealing substrate 804, and the sealing agent 805. The space 807 alsoincludes a structure filled with the sealing agent 805 in addition tothat filled with inert gas (such as nitrogen or argon).

It is preferable to use epoxy resin for the sealing agent 805. Inaddition, it is desirable to use a material that permits moisture oroxygen to transmit through thereof as less as possible. Further, as amaterial that is used for the sealing substrate 804, a plastic substratecontaining FRP (Fiberglass-Reinforced Plastics), PVF(polyvinylfluoride), Mylar, polyester, or acrylic can be used besides aglass substrate and a quarts substrate.

In this way, the light-emitting device having a light emitting elementcan be obtained according to the present invention.

Embodiment 8

In the present embodiment, various electronic devices completedincluding a light-emitting device, for example, formed according toEmbodiment 7 will be described.

As electronic devices manufactured with the use of a light-emittingdevice according to the present invention, devices such as a videocamera, a digital camera, a goggle-type display (head mount display), anavigation system, a sound reproduction device (such as an in-car audiosystem or an audio set), a computer, a game machine, a personal digitalassistant (such as a mobile computer, a cellular phone, a portable gamemachine, or an electronic book), an image reproduction device equippedwith a recording medium (specifically, a device equipped with a displaydevice that can reproduce a recording medium such as a digital versatiledisc (DVD) and display the image) can be given. FIGS. 9A to 9Gshow-specific examples of such electronic devices.

FIG. 9A is a display device, which includes a frame body 2001, a support2002, a display portion 2003, a speaker portion 2004, and a video inputterminal 2005. A light-emitting device formed according to the presentinvention is used for the display portion 2003 to manufacture thedisplay device. The display device includes all devices for displayinginformation such as for a computer, for receiving TV broadcasting, andfor displaying an advertisement.

FIG. 9B is a computer, which includes a main body 2201, a frame body2202, a display portion 2203, a keyboard 2204, an external connectionport 2205, and a pointing mouse 2206. A light-emitting device formedaccording to the present invention is used for the display portion 2203to manufacture the laptop personal computer.

FIG. 9C is a mobile computer, which includes a main body 2301, a displayportion 2302, a switch 2303, an operation key 2304, and an infrared port2305. A light-emitting device formed according to the present inventionis used for the display portion 2302 to manufacture the mobile computer.

FIG. 9D is a portable image reproduction device equipped with arecording medium (specifically, a DVD reproduction device), whichincludes a main body 2401, a frame body 2402, a display portion A 2403,a display portion B 2404, a recording medium (such as a DVD) readingportion 2405, an operation key 2406, and a speaker portion 2407. Thedisplay portion A 2403 is used mainly for displaying image informationwhile the display portion B 2404 is used mainly for displaying characterinformation, and a light-emitting device formed according to the presentinvention is used for display portion A 2403 and display portion B 2404to manufacture the portable image reproduction device equipped with therecording medium. The image reproduction device equipped with therecording medium further includes a home game machine.

FIG. 9E is a goggle-type display, which includes a main body 2501, adisplay portion 2502, and an arm portion 2503. A light-emitting deviceformed according to the present invention is used for the displayportion 2502 to manufacture the goggle-type display.

FIG. 9F is a video camera, which includes a main body 2601, a displayportion 2602, a frame body 2603, an external connection port 2604, aremote control receiving portion 2605, an image receiving portion 2606,a battery 5607, a sound input portion 2608, an operation key 2609, andan eye piece 2610. A light-emitting device formed according to thepresent invention is used for the display portion 2602 to manufacturethe video camera.

FIG. 9G is a cellular phone, which includes a main body 2701, a framebody 2702, a display portion 2703, a voice input portion 2704, a voiceoutput portion 2705, an operation key 2706, an external connection port2707, and an antenna 5208. A light-emitting device formed according tothe present invention is used for the display portion 2703 tomanufacture the cellular phone.

As described above, a light-emitting device formed according to thepresent invention is quite widely applied. In addition, since thelight-emitting device has a light extraction efficiency which isincreased by providing a reflector, the light-emitting device permitsthe driving voltage to be decreased as compared to a light-emittingdevice formed without providing a reflector. Therefore, it is possibleto reduce power consumption and extend a lifetime of electronic devicesin all fields by applying this light-emitting device.

Since the arrangement density of a reflector can be increasedindependently of a light-emitting region by implementing the presentinvention, it is possible to provide a light-emitting device that has aluminance improved more than ever before.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the present invention hereinafterdefined, they should be construed as being included therein.

1-12. (canceled)
 13. A light-emitting device comprising: a substrate; areflector having a plurality of openings formed over the substrate; anda light-emitting element formed over the reflector, wherein thereflector is overlapped with the light-emitting element.
 14. Thelight-emitting device according to claim 13, wherein shapes of theplurality of openings of the reflector are hexagonal, quadrangle, ortriangular.
 15. The light-emitting device according to claim 13, whereinlight of the light-emitting element is emitted through the plurality ofopenings of the reflector.
 16. The light-emitting device according toclaim 13, wherein the light-emitting element is electrically connectedto a thin film transistor.
 17. The light-emitting device according toclaim 13, wherein a slope angle of the reflector is from 40° to 80°. 18.The light-emitting device according to claim 13, wherein a slope angleof the reflector is from 60° to 85°.
 19. The light-emitting deviceaccording to claim 13, wherein the reflector comprises a materialselected from the group consisting of silver (Ag), aluminum (Al),tantalum (Ta), niobium (Nb), molybdenum (Mo), copper (Cu), magnesium(Mg), nickel (Ni), and lead (Pb).
 20. An electronic device comprisingthe light-emitting device according to claim 13, wherein the electronicdevice is selected from the group consisting of a display device, acomputer, a portable image reproduction device, a goggle type display, avideo camera and a cellular phone.
 21. A light-emitting devicecomprising: a substrate; a reflector having a plurality of openingsformed over the substrate; and a light-emitting element formed over thereflector, the light-emitting element comprising a first electrode, alayer including a luminescent material and a second electrode, whereinthe reflector is overlapped with the light-emitting element.
 22. Thelight-emitting device according to claim 21, wherein shapes of theplurality of openings of the reflector are hexagonal, quadrangle, ortriangular.
 23. The light-emitting device according to claim 21, whereinlight of the light-emitting element is emitted through the plurality ofopenings of the reflector.
 24. The light-emitting device according toclaim 21, wherein the first electrode of the light-emitting element iselectrically connected to a thin film transistor.
 25. The light-emittingdevice according to claim 21, wherein a slope angle of the reflector isfrom 40° to 80°.
 26. The light-emitting device according to claim 21,wherein a slope angle of the reflector is from 60° to 85°.
 27. Thelight-emitting device according to claim 21, wherein the reflectorcomprises a material selected from the group consisting of silver (Ag),aluminum (Al), tantalum (Ta), niobium (Nb), molybdenum (Mo), copper(Cu), magnesium (Mg), nickel (Ni), and lead (Pb).
 28. An electronicdevice comprising the light-emitting device according to claim 21,wherein the electronic device is selected from the group consisting of adisplay device, a computer, a portable image reproduction device, agoggle type display, a video camera and a cellular phone.
 29. Alight-emitting device comprising: a substrate; a reflector having aplurality of openings formed over the substrate; and a light-emittingelement formed over the reflector, wherein the reflector is overlappedwith the light-emitting element, and wherein an arrangement density ofthe reflector is from 20 to 80%.
 30. The light-emitting device accordingto claim 29, wherein shapes of the plurality of openings of thereflector are hexagonal, quadrangle, or triangular.
 31. Thelight-emitting device according to claim 29, wherein light of thelight-emitting element is emitted through the plurality of openings ofthe reflector.
 32. The light-emitting device according to claim 29,wherein the light-emitting element is electrically connected to a thinfilm transistor.
 33. The light-emitting device according to claim 29,wherein the reflector comprises a material selected from the groupconsisting of silver (Ag), aluminum (Al), tantalum (Ta), niobium (Nb),molybdenum (Mo), copper (Cu), magnesium (Mg), nickel (Ni), and lead(Pb).
 34. An electronic device comprising the light-emitting deviceaccording to claim 29, wherein the electronic device is selected fromthe group consisting of a display device, a computer, a portable imagereproduction device, a goggle type display, a video camera and acellular phone.